Merge commit '7621e2f8dec938cf48181c8b10afc9b01f444e68' into beta

submodules/lottie-ios/Sources/Public/ImageProvider/AnimationImageProvider.swift

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+//
+//  LottieImageProvider.swift
+//  lottie-swift
+//
+//  Created by Brandon Withrow on 1/25/19.
+//
+
+import CoreGraphics
+import Foundation
+
+/// Image provider is a protocol that is used to supply images to `AnimationView`.
+///
+/// Some animations require a reference to an image. The image provider loads and
+/// provides those images to the `AnimationView`.  Lottie includes a couple of
+/// prebuilt Image Providers that supply images from a Bundle, or from a FilePath.
+///
+/// Additionally custom Image Providers can be made to load images from a URL,
+/// or to Cache images.
+public protocol AnimationImageProvider {
+  func imageForAsset(asset: ImageAsset) -> CGImage?
+}